This invention relates to an erasable optical disk and an optical information recording and reproducing apparatus recording and reproducing information by irradiating a laser beam to the optical disk, and more particularly to management of a defective sector of the optical disk.
A method of managing a defective data sector of an optical disk is disclosed in, for example, JP-A-61-20271. FIG. 4 shows the arrangement of alternate tracks in the optical disk. Referring to FIG. 4, the optical disk includes alternate tracks A, ordinary tracks B for recording data, a secondary alternate track area C, and sector identifier fields D having addresses recorded thereon. FIG. 5 is a block diagram of an optical information recording and reproducing apparatus for recording and reproducing information on and from the optical disk including the alternate tracks shown in FIG. 4. Referring to FIG. 5, the optical information recording and reproducing apparatus includes a sector address reproducing circuit 19, a data reproducing circuit 20, a target sector address register 21, a sector address coincidence detecting circuit 22, a data recording gate signal circuit 23, a data reproducing gate signal circuit 24, a defective sector detecting circuit 25 for detecting a defective sector, an alternate track setting circuit 26, and a sector deleting gate signal circuit 27 for writing an identification mark on a defective sector.
In the optical information recording and reproducing apparatus having the structure described above for recording and reproducing information on and from the above-mentioned optical disk having the track assignment shown in FIG. 4, a coincidence signal is generated from the sector address coincidence detecting circuit 22 when the output signal of the target sector address register 21 is coincident with that of the sector address reproducing circuit 19. The coincidence signal generated from the sector address coincidence detecting circuit 22 is applied to the data recording gate signal circuit 23 or the data reproducing gate signal circuit 24, and, in response to the application of the output signal of the data reproducing circuit 20 or that of the data recording gate signal circuit 23 or that of the data reproducing gate signal circuit 24, the defective sector detecting circuit 25 detects a defective sector by detecting, for example, a sector address error of the sector identifier field or an error syndrome detected as a result of decoding an error detecting and correcting code in the data reproducing circuit 20. When such a defective sector is detected, the alternate track setting circuit 26 calculates the alternate track associated with the data track to which the defective sector belongs, and data on the defective sector is recorded on an unused sector of the alternate track. Then, the sector deleting gate signal circuit 27 overwrites a delete signal on the data field of the defective sector. In the reproducing operation, this delete signal overwritten on the data field of the defective sector is detected to indicate that the defective sector is substituted by one of the sectors of the alternate track.
Thus, in the above-mentioned optical disk, such an alternate track is provided to each of track blocks so as to shorten the time required for access to any one of the alternate tracks.
When the optical disk having the track assignment described above is of the erasable optical disk in which data is repeatedly erased and recorded on the same data sector, the defective sector detecting circuit 25 can detect a defective sector by detecting an address error of the sector address identifier field. However, when the defect exists in the data field of the defective sector, data is recorded on the data field of the defective sector because the delete signal recorded on the data field cannot be detected before the sector address in the sector address identifier field is detected. Consequently, the above type optical disk has had such a problem that the alternate operation of the same defective sector performance again, and, due to this requirement, an extra processing time for this operation is additionally required, resulting in a reduced speed for access.